The present invention relates to a tape-like coated optical fiber in which a plurality of optical fiber strands colored for discrimination are arranged side by side on a plane and a tape coating is applied onto the outer periphery of the side-by-side arrangement of the optical fiber strands so as to integrate the optical fiber strands with each other.
Generally, a tape-like coated optical fiber has such a configuration that a plurality of optical fiber strands each having one or more of protection layers of ultraviolet curable resin provided on an outer periphery of an optical fiber glass are arranged side by side on a plane and a tape coating of ultraviolet curable resin is applied onto an outer periphery of the optical fiber strands so as to integrate the optical fiber strands with each other.
In such a tape-like coated optical fiber, it is necessary that the tape-like coated optical fiber is separated into optical fiber strands and the thus separated optical fibers are discriminated from each other in measurement of optical fiber transmission characteristics, attachment of a connector for conversion from a multi-core coated optical fiber into single-core coated optical fibers, or the like. There has been proposed a tape-like coated optical fiber, as disclosed, for example, in Japanese Patent Unexamined Publication No. Sho-63-281109, in which a layer colored with ultraviolet curable ink is provided on a coating layer of ultraviolet curable resin of each of the optical fiber strands and a peeling-off property is given to the colored layer.
FIG. 1 is a cross section of such a tape-like coated optical fiber. In the drawing, reference numeral 1 designates an optical fiber glass; 2, a coating layer of ultraviolet curable resin; 3, a layer colored with ultraviolet curable ink; and 4, a tape coating of ultraviolet curable resin.
In the foregoing tape-like coated optical fiber shown in FIG. 1, in view of separation of the coated optical fiber into single-core optical fibers and discrimination of the separated optical fiber strands, endeavor has been made so as to reduce adhesion between the optical fiber strands and the tape coating by providing the colored layer on the ultraviolet curable resin coating layer of each of the optical fiber strands.
If such a tape-like coated optical fiber is exposed to high temperature and humidity, however, there have been problems in that since a non-cured component and a residual initiator evaporate from each of constituent materials as volatile components and a tape material exists in the upper layer, vapor permeated through the tape coating adheres to the partially remaining initiator and sensitizer to partially form dew to cause partial peeling-off between the tape coating and the optical fiber strands which are weak in adhesion so that not only abnormality is caused in the exterior but bending is locally generated in the optical fiber to thereby deteriorate the transmission characteristics.